Stylus

1. A stylus, comprising: a casing comprising an opening; a push rod disposed in the casing; a pen head fixed on an end of the push rod, wherein at least a part of the pen head is exposed from the casing; a reflector coupled to the push rod; and a linkage mechanism disposed in the casing, wherein an end of the linkage mechanism is fixed on the casing, the linkage mechanism connects the reflector to the push rod, such that when the pen head is pushed into the casing, a moving distance of the reflector is greater than that of the pen head, and the reflector is exposed from the opening.

2. The stylus of claim 1 , further comprising: a baffle disposed in the casing; a sleeve fixed at another end of the push rod; and a spring wrapped to the sleeve and disposed between the push rod and the baffle, such that the reflector is pushed and hidden in the casing when the pen head is pushed outward by an elastic force generated by the spring.

3. The stylus of claim 2 , wherein the sleeve comprises a cavity, and the push rod is coupled to the cavity.

4. The stylus of claim 2 , wherein the sleeve comprises a support flange, and the spring is disposed between the support flange and the baffle.

5. The stylus of claim 1 , wherein the linkage mechanism comprises: a first linkage having a first pivot end and a second pivot end opposite to each other, and two first pivot portions disposed between the first pivot end and the second pivot end; two second linkages respectively connecting the first pivot portions to the push rod; a third linkage connected to the reflector; and a fourth linkage connecting the third linkage to the second pivot end.

6. The stylus of claim 5 , wherein the push rod comprises two second pivot portions, and the second linkages respectively connect the first pivot portions to the second pivot portions.

7. The stylus of claim 5 , wherein the casing comprises a third pivot portion, and the first pivot end is coupled to the third pivot portion.

8. The stylus of claim 5 , wherein a distance between the second pivot end and the first pivot portions is even to or greater than a distance between the first pivot end and the first pivot portions.

9. The stylus of claim 5 , wherein the third linkage is coupled to the push rod.

10. The stylus of claim 9 , wherein the third linkage is made of a light-absorbing material.